Machining processes typically require a workpiece, such as a camshaft, to be mounted between a headstock and a tailstock each carried by a workpiece carriage disposed for linear movement along ways, slides or tracks carried by the bed of a machine tool. The workpiece is usually carried by the headstock and tailstock for rotational movement about an axis of rotation passing through at least a part of the workpiece. The worktool for such machining processes, which may be a grinding wheel for example, is also mounted to or carried by a carriage which is also disposed for linear movement along ways, slides or tracks carried by the bed of the machine tool. A grinding wheel worktool would be carried by its tool carriage for rotation about its axis of rotation.
The linear movement required for such carriages is usually such that the carriages are moved from home position in a first direction, possibly in increments, and then returned in the opposite direction to or towards the home position, possibly in increments also. It is commonplace to accomplish such linear carriage motion through conventional mechanisms such as ball screws, linear motors, or similar devices. Some worktool carriages are, in turn, mounted upon another carriage so that the worktool can be moved in directions parallel to the workpiece as well as in directions perpendicular too the workpiece.
Relative movement between such carriages and their respective supporting ways, slideways, tracks or the like also requires the use of bearings or bearing surfaces on or between the carriage and its supporting structure. The incorporation of such bearings and/or bearing surfaces, however, more often then not may also permit the carriage to twist and turn in horizontal and vertical and rotational manner with respect to its mounting on the machine tool; especially in reaction to forces developed when the tool is in contact with the workpiece. Twisting and turning of the carriage and the workpiece carried by the carriage with respect to the worktool often results in improperly machined and unacceptable workpieces.
The stiffer the bearing arrangement between the carriage and its support structure the better the machining. It has been proposed to increase the stiffness of relatively movable machine tool components by utilizing hydrostatic type bearings between relatively moving surfaces thereof. However, hydrostatic bearing design quite often requires the creation of secondary surfaces in a plane or planes parallel to the intended bearing surfaces and the application of hydrostatic fluid to those secondary surfaces to generate fluid pressure in directions opposite to that of the fluid pressure between the intended bearing surfaces in order to obtain an effective hydrostatic bearing arrangement and maintain an optimal gap spacing between the primary bearing surfaces. the creation of those secondary surfaces and the provision of passageways to provide hydrostatic fluid thereto not only results in design problems for the machine components but also may unduly and unacceptably increase the cost of machining the component.
It has also been proposed to utilize linear electromagnetic type drives (i.e., linear motors) to effect movement of the machine tool carriages on these respective slides, slideways or tracks. However, some such linear motors general considerable attractive forces between their coil assemblies and magnetic plates and therefore require heavy duty bearing arrangements in order to function properly and effectively.